Gwynne Dyer
Gwynne Dyer is a commentator on international affairs based in London

Gwynne Dyer: Extreme weather a little payback for temperate emitters

Photo / NZ Herald
Photo / NZ Herald

The standard climate change predictions said people in the tropics and the sub-tropics would be badly hurt by global warming long before those living in the temperate zones felt much pain at all.

That was unfair, because it was the people of the rich countries in the temperate zone - North America, Europe and Japan, mainly - who industrialised early and started burning large amounts of fossil fuel as long as two centuries ago. That's how they got rich. Their emissions of carbon dioxide over the years account for 80 per cent of the greenhouse gases of human origin that are now in the atmosphere, causing the warming, yet they get hurt least and last.

Well, what did you expect? The gods of climate are almost certainly sky gods, and sky gods are never fair. But they have always liked jokes, especially cruel ones, and they have come up with a great one this time. The people of the temperate zones are going to get hurt early after all, but not by gradual warming. Their weather is going to get more and more extreme: heat waves, blizzards and flooding on an unprecedented scale.

"In 2012 we had the second wettest winter on record and this winter is a one-in-250-years event," British opposition leader Ed Miliband told The Observer newspaper. "If you keep throwing the dice and you keep getting sixes then the dice are loaded. Something is going on."

The "something" is abrupt climate change. In Britain, it's an unprecedented series of great storms blowing in off the North Atlantic, causing disastrous floods. In the United States and Canada, it's huge blizzards, ice-storms and record low temperatures that last much longer and reach much further south than normal. The extreme weather trend in North America and Europe is less than five years old, so the science that might explain it is still quite tentative. The first hypothesis that sounded plausible, published in 2012 in Geophysical Letters, blamed a slowing of the northern polar jet stream.

The paper, entitled "Evidence linking Arctic amplification to extreme weather in mid-latitudes," was written by Jennifer Francis of Rutgers University and Stephen Vavrus of the University of Wisconsin-Madison.

They start with the fact that the Arctic has been warming faster than anywhere else, so the temperature difference between the Arctic air mass and the air over the temperate zone has been shrinking. Since that temperature difference is what drives the jet stream, a lower difference means a slower jet stream.

A fast jet stream travels in a pretty straight line from west to east, just like a mountain stream goes pretty straight downhill. A slower jet stream, however, meanders like a river crossing a flood plain - and the big loops it makes extend much further south and north than when it is moving fast.

In a big southerly loop, you will have Arctic air much farther south than usual, while in a northerly loop relatively warm air from the temperate air mass extends into the Arctic. Moreover, the slower-moving jet stream tends to get "stuck", so that a given kind of weather - snow, or rain, or heat - will stay longer.

Hence the "polar-vortex" winter in North America this year, the record snowfalls in Japan in 2012 and again this winter, the heat waves in the eastern US in 2012 - and the current floods in Britain.

"They've been pummelled by storm after storm this winter [in Britain]," said Jennifer Francis at the American Association for the Advancement of Science conference in Chicago last week. "It's because the pattern this winter has been stuck in one place ever since early December."

There's no reason to think that it will move on soon, either.

Gwynne Dyer is an independent journalist published in 45 countries.

- NZ Herald

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